High-frequency electron discharge apparatus



' L ful l L. F. SORG 2,678,404

HIGH-FREQUENCY ELECTRON DISCHARGE APPARATUS May 11, 1954 Filed Dec. 30, 1949 INVENTOR [L0 YD E 50/?6 current' velocity changes.

-.direction.

different frequency outputs.

Patented May 11 1954 HIGHJ REQUENCY ELECTRON DISCHARGE APPARATUS Lloyd F. Sorg, Redwood Gity, Califi, assignor to The Sperry Corporation, :a corporation of Delaware Application December 30, 1949,'-Serial No. 135.867

4 Claims.

This invention relates generally to the production of ultra-highfrequency .waves and, more particularlyto a novel form ofvelocity modulation electron discharge device.

Electron tube structures employing a single cavityresonator and functioning according to velocity and density modulation-principles are 'known. In such devices an electron beam is projected in. afirst traverse of the resonator during which time the electron beam undergoes re- A reflecting electrode positioned beyond the'resonator and in the-path of the velocity modulated beam is effective for reversing the direction-'ofthe beam. In the space between the resonator and the reflecting electrode the velocity mo'dulated electron beam becomes density modulated withthe faster moving electrons'transversing-a greater distance than the slowermoving electrons before being reversed in In this manner the velocity modulated beam undergoes reflection fieldbunching withthe formation of groups of electrons. The

potential distribution is such as to .reproject the density modulated beam back through theresonator with the beamgiving up energy to the resonator to sustain oscillations therein. Such devices -have :generally;.been termed reflex klystrons.

According to the: present invention an electron discharge deviceis provided with plural resona- -.tcrs'cooperating with a unitary electron gunan'd reflecting electrode and operating accordingvto velocity modulationaprinciples. .By suitable choice of operating parametersany ,oneof theplural resonators -may..b.e excited into oscillation at a given time. With the resonators dimensioned to 1 resonate at different frequencies a compactand efficient electron tube structure is provided suitable'forgenerating alternatively a plurality of By properly varying the operating conditions of the device any one of "the resonators may be excited independently'of'the other resonators to generate cyclically varying electromagnetic waves having a frequency correspondingto the resonant frequency of a particular resonator.

Accordingly it is an object of the present invention to provide an efficient and compact electron discharge apparatus suitable for alternatively generating'different frequency signals.

Another object isto. provide an improved electronicswitching-device wherein electromagnetic oscillations having diiferent frequencies are generated in response'to electrical impulses of' 'different magnitudes.

Other objects and advantagesof this; invention will become apparent from the specification, taken in connection 'withthe accompanying draw- .ings wherein the invention is embodiedin concrete form.

In the drawings,

Fig; 1 .is an elevational view, partly in crosssection, of an electron tubestructure according to the present invention.

Fig. 2 is cross-sectional plan view of the device of Fig. .1 taken along line 2-2 of Fig. 1.

Fig.3 is a fragmentary elevational view, partly in vcross-section, showing a modification of the device. of Fig. .1.

Referringto Figs-1 and .2, a velocity modula- .tion-zdevice H is shown havinga source of electrons consisting of an oxide-coated cathode button I2, which maybe energized by heater elementit. Surrounding the heater element l3-is a heater housing member l4 attached to a focusing shield 16. The cathode button 12 is secured to'thefocusingshield l6 and positioned within the aperture thereof by means of substantially tangentially disposed wires (not'shown), therespective ends of whichare fastened, as by weld- .ing,.toithe button I2 and shield [6.

An insulating ringxl8 rests in contact along its *lowersurface with a-radially-extending flange l1 "ofthe focusing. shield I6 and along its upper internalsurface with lip portion l9'of an-aperttured disk 2!.

Disk 2| is secured,- as by spot welding, tothe upper portion 22 of the shell 23.

Thus,by the arrangement, the cathode button I2 is properly centered along the axis of the tube II by the cooperation betweenthe insulating'ring l8, shield l6 and disk 2|. In addition, theinsulating ring l8 serves to electrically "isolate. thecathode'button l2 from the shell '23.

.In'order to provide electrical contact with the cathode button lZand shield It, leads 24, 26 and 21 having portions'28, 29 and 31, respectively, which-are formedpreferably of a material, such .as Kovar, having a linear coeflicient of thermal :expansion approximating that of .a-suitable glass, are made to pass through-a vitreous platform 32.

To support the platform 32 within theshell 23there1is provided an .annular support member .33 havinga curved flange portion 34 which is secured to the platform 32. The lower end of the member 3.3 is formed with'a-lip portion 3-6 whichissecured to "the shell 23. Thus, in the lower portion of the'tube I I, platform'32; annular support member 33* and the portion of shell 23 extendingab'ovethe lip tii constitute a vacuum envelope, with the respective connections :being formed in agvacuum-tight manner.

A tube 31, aligned with the longitudinal axis of the tube I l, is rigidly attached to and supported by the upper portion 22 of the shell 23. Adjacent the other end of tube 3'! are two means defining an electromagnetic field, such as resonators 33, 39, with resonator 38 having an electronpermeable region or gap defined by grids 4|, 42. Owing to the shape of tube 31, resonator 3B is provided with a slightly reentrant configuration. Similarly, resonator 39 has an electron-permeable region or gap defined by grids 43, M.

Both resonators 38, 39, are constituted by stacking and interconnecting suitably-formed sheets or laminations of metal. Partly surrounding the tube 31 and xtending along the axis of tube ii are metallic laminations or plates tit-50, which may be joined as by brazing with a silvercopper alloy. Plate 49 serves to define a part of the wall surfaces for both resonators 38, 39 as well as support rings 52, 53 to which are secured grid; 52, 53. Thus, an electron drift space or tube 5a is formed between grids s2, 43. Plate 50 supports grid l and by reason of its exposed lower surface forms a part of the wall for resonator 39.

End plate is suitably apertured to provide an electromagnetic energy window for coupling energy from both resonators 38, 39.

In view of the fact that the upper end of tube 37, plates 33- 59, rings 52, and end plate 56 form the walls of resonators 33, 39, these parts are preferably constituted of highly conductive surfaces. This may be accomplished by employing copper or copper-plated materials.

Plates 41435] are each joined to one another in a vacuum-tight manner, as discussed above. In addition, the connections of the tube 3?! to the lower plates 46 as well as the upper portion 22 of the shell 23 are similarly vacuum-tight joints.

A reflector electrode 5'? is rigidly joined to a dish-shaped member 58 which is supported by a reflector lead 59 rigidly secured thereto. The lead 59 passes through glass seal 6| to effect electrical contact with cap 62.

A cylindrically-shaped sleeve 63 is attached at its upper end to a frusto-conically-shaped member 64, which member 54 is centrally-apertured and joined to seal (ii. The connections between the reflector lead at, the seal 5!, the frusto-conically-shaped member 54, and the sleeve 63 are all effected in a vacuum-tight manner. In a similar manner the cooperating part of the radiallyextending flange portion Bl of sleeve 63 is joined to plate 50.

To electrically isolate the cap 62 from the cylindrical sleeve 63 and the remainder of the tube i i, there is provided an annular insulating member '66. In joining the cap 62 to the insulating member 65 the end portion of the cap 62 may be spun over the insulating mmber 55.

To energize the heater element l3 leads 24, 26 are connected to a suitable source of potential, such as battery 68. The cathode button I2 is maintained at a negative potential with respect to the smoother grid 35 and resonators 38, 39 by means of a suitable source of potential, such as battery 89 andvoltage-divider ll. Tap 12 of the voltage-divider ll connects with lead 21 by means of external lead 13. The reflector electrode 51 is maintained at a potential equal to or below the value of the potential applied to the cathode button i2 by movable contact or tap i l and external lead ll, which is connected through switch 76 to cap 62.

While tap 14 is effective through adjustment for varying the potential applied to the reflector electrode 51, the voltage of this electrode 51 may be rapidly varied between two values by means of a further movable contact or tap 78. The switch It is effective for applying either of two voltages to the reflector electrode 5?. This arrangement will be discussed more fully below.

To couple electromagnetic energy from the resonators 38, 39, electromagnetic coupling means, such as wave guide 79, are provided. This wave guide #9 is preferably formed with highly conductive internal surfaces, which may be accomplished by fabricating wave guide 19 from copper or a copper plated material, in order to effect an efficient transfer of energy. The end of the wave guide [9 is closed by means of a window frame 8!, in which there is included a glass window 32. To facilitate the connection of the window frame iii to the wave guide 79 a ring 83 is provided, which initially may be secured to the wave guide 79. Enlarged end portion 84 of the window frame 8! may be joined, as by soldering with a copper-silver alloy, to the ring 83. Surrounding the frame 8! is a housing member 86 joined to the ring 83, with the connection preferably being made with solder having a relatively low melting point in order to ensure that the connection between the enlarged end portion 84 of the frame 8i and the ring 33 is not thereby disturbed. At the end of the housing member 86 adjacent the glass window 32 is positioned an apertured end plate 81 rigidly joined thereto.

In view of the fact that the wave guide l9. window frame 8|, glass window 82 with the cooperating action of ring 83 constitute a portion of the vacuum envelope of the tube i I, all these connections are formed in a vacuum-tight man ner. In addition, the wave guide 19 is joined to the metal plates 46, 41 as well as the flange portion 6i of the sleeve 63 in vacuum-tight connections.

Owing to the configuration of th window frame 8!, the joining of this part to the wave guide 79 is facilitated by connecting the frame 8| to the rin 83 at'a point relatively far removed from the glass window 82, with the possibility of cracking of or other damage to the glass window 82 being minimized. Thus, the shape of the window frame 8| is such as to provide a relatively long heat fiow path from the enlarged end portion 84 to the glass window 82.

In operation, the electrons emanate from the cathode button l2 and under the influence of an accelerating potential, maintained in part by the battery 69, accelerate toward the smoother grid 35 and traverse the tube 37. As a function of the magnitude of the voltage applied to the reflector electrode 51 either one of the resonators 38, 39 may be effective in the velocity modulation process.

In the event that the potential at which the reflector 57 is maintained is suitable for energization of resonator 39, the electrons after passing through tube 31, the gap defined by grids 4|, 42 and drift space 54, traverse the grids 43, M of resonator 39. In the space between the grid 44 and the reflector electrode 51, the electrons of the beam will experience reflecting field bunching to be reversed in direction and returned to the resonator 39 to deliver electromagnetic energy thereto.

Accepted theories of the foregoing action based on velocity modulation principles are explained fully in Fig. 2 of United States Patent N0. -2.,250;5.11,2issuedJu1y229, 1941, toiRussellil-l.

.ithantthe averagettime to return to-theresonator 39. An electron leavingthe resonatorl33 at :a-timewhen-the radio. frequency voltage therein .iszero-v and changingfrom acceleration to decelerationrequires an average transit time. An electron which passes .the resonator 39 earlier in'the cycle is acceleratedwand requires. alonger timeto return. Moreover, an electron. that traverseszthe resonator 39 later in the cycle requires less than the average transit time. All these electrons return to the resonator in a bunched condition at alatertime. 'Thus,.hy the velocity modulation action of the. resonator 39 grouping -of':the-electrons of the beam results, and as a consequence, the uniform flow of beam current is converted into an equivalent direct; current with a'superimposed alternating component.

Since a maximum retarding field is required formaximum energy transferred from the bunched beam, the transit time. for an electron that enters the. reflecting field with average velocity must .correspond'to one quarter cycle .lessthan an integral number of cycles.

With regard to resonator 38, it will be noted that electrons passing grid 42 thereof are not immediately brought. under the influence of the reflection field. Such electrons traverse the drift spacei l, and the gap of resonator 39., defined bya.g-;1'ids,.4=3:, 44' before. entering the reflection field provided in part by the reflector, electrode 51. The electrons in passing through the electron permeable region of the resonator 38 are subjected. to velocity modulation in their initial transit, that is, from the cathode button E2 toward. the reflector electrode 51. After passing the-grid 42, such electrons passthrough the field f-ree drift. space 54 and grids 43., 4.4;to undergo field free bunching prior to the time reflection field bunching occurs. The, expression "fieldfree, as. used; above, and as used; through out the. restof the. specification and chaims, is intended. to. mean free of any reflection fields and isnot. intended: .to excludemagnetic fields as might be employed in focussin the electron beam as isfound in. some electronv discharge ap paratus.

In the region between the grid 44. and the reflector electrode 5.1- the velocity modulated electrons experience reflection field bunching, with thefaster moving electrons traversing a greater distance before being reversed in direction. As a result, a. bunchedelectron beam is" formed.

Afterpassing grid. 44 the electron. beam, hay.- ingybeen reversedin direction, passes. through the grids 44, 43 and. drift space 54 before traversing thegapof resonator 38 defined by grids 4|,

42 where energy" is extracted by resonator 38 to; sustain oscillations therein.

Thus, the electron beam in the case of excitation of resonator 38 undergoes reflection field bunchin as well as field-free bunching, the latter, occurring between grids 43., 44. and in drift space. 54. The fieldefree bunching, issimilar to the. process whichoccurs for instance, ina dual resonaton-klystron,sue-has shown inII. S. Patent No; 2,242,275,; entitled Electrical;v Translating System and Methods in the name-of IR; Varian.

A review of both-types of bunching in-physically separate andrdistinct velocity modulation devices reveals that the current vdistribution'iin a reflected hunch is similartothat in the fieldfree case, butthatthe manner in which the electrons reach this distribution is. decidedlydiffierent. In the field-free case an infinite current peak exits prior to the time the electrons arrive at the. gap of the. output or energy-extracting resonator. The. electrons traveling inthe bea'm pass one another, with-theinfinite currentpeak separating toform a large but finite current peak between two diverging infinitecurrent peaks.

In reflection field bunching, which occurs-inn reflex klystron, a simil iar current distribution results. However, there is no single infinite current peak formed-prior tothe formationof a double infinite current peak. If the-magnitude of the velocity modulation remains the same, in-

troducing both types of bunching :the same tube results-in a decreased output owing to: the fact that the two effects are out of phase.

Thus, an important consideration .of the instant invention is that of providing a minimum length drift space, such as drift space 54, which is approximately the samein length as the-extent of either of thev electron permeable-regions"of resonators 38 and 39. This: is desirable inordier to ensure a relatively large magnitude of output power from resonator 38. This consideration shouldbe consistent with-'mod'eseparation, as discussed below.

Another consideration with regard: to the instant invention is that of maintaining amassimum separation between themodes atosci-ll'ation of the separate resonators 38', 39. In Klystron Tubes," A. E. Harrison, McGraw-Hill Book Com:- pany, Inc., 1-947. at page 98 there is shown in Figs. 7-8, apower output vs. reflector: voltage characteristic. The actionof the reflex kllystron is such that distinct modes of oscillation: occur at different values of the reflector voltage-.- 0scillations take place with. varying magnitudes of reflector voltages when the transit time for the-electrons has changedby an amount equiv -alentto one complete cycle. In the instant device H, in order to prevent both resonators'iis,

coaxial transmission-lines 91, 9'2 -with their coupling loops 9 3; 94 respectively, are employed for coupling energy from resonators 38-; 39 respectively.

An important advantage of the. laminated construction. of. the; side. walls; ofath'e: resonators 38,39 asshown'in Figs; 1 andz2istha-t resonators vices suitable for providing a wide range of different frequencies are more readily constructed.

It is, of course, understood that the coaxial transmission lines 9!, 92 may be employed in place of wave guide 19 for coupling energy from the resonators 38, 39 of Figs. 1 and 2. Similarly, the wave guide 19 may be employed for a similar purpose with the resonator construction of Fig. 3.

While no tuning mechanism has been shown for adjusting the frequency during operation of the resonators 38, 39, it was found possible by pre-tuning the resonators 38, 39 during fabrication to obtain a frequency separation of 180 megacycles between the resonator frequency of resonators 38, 39, with operating frequencies having wavelengths in the neighborhood of 3 centimeters. The pre-tuning of the upper resonator 39, for instance, was accomplished by adjusting the spatial separation of the grids 43, 44 with a hydraulic press.

It is, of course, understood that the invention may be employed with vastly different operating frequencies as well as significantly different frequency separations between resonators, such as resonators 38, 39.

If desired tuning mechanism may be employed in conjunction with the resonators 38, 39. For

instance, the tuner shown in application Ser. No. 725,106, in the name of Marvin Chodorow, filed January 29, 1947, issuing as Patent No. 2,617,071 on November 4, 1952, may be employed. Also,

if desired, other tuning arrangements similar to those shown in U. S. Patent No. 2,280,824, en-

titled Radio Transmission and Reception, is-

nitude, whereas a signal having a different frequency may be generated as a function of a similar-type potential of a different selected magnitude. Such potential may, for instance, be applied to the reflector electrode 51 in substitution for the voltage-divider "H, switch 16 and structure associated therewith.

While the invention has been described in connection with two resonators 36, 39, it is of course understood that a multi-resonator structure may be employed, in which the separate resonators have spaced resonant frequencies. With such an arrangement, to separately excite the various resonators, a multi-switch arrangement would be suitable for obtaining the proper reflector voltage from a voltage divider such as voltage divider H.

While the invention has been described in terms of a reflector voltage variation to obtain the selective energization of the resonators 33, 39, it is of course understood that other operating voltages might be systematically altered to obtain the same result. For instance, theaccelcrating voltage, such as the voltage applied by the smoother grid 35 and the cathode button i2 by means of voltage divider ll and tap '12, might be varied to separately and selectively excite resonators 38, 39. In such case, a switch similar to switch 16, together with cooperating movable contacts associating with the voltage divider H, might be introduced into the external lead 73.

It is also apparent that both the reflector and the accelerating voltages might be adjusted simultaneously to diiferent values to achieve the present invention.

While the internal parts of tube ll have been shown in Figs. 1 and 3 as symmetrically disposed about the longitudinal axis of the tube II, it is understood that Figs. 1 and 3 may be regarded essentially as figures of translation rather than figures of revolution.

It appears that many changes could be made in the above-described construction including, for instance, the resonator construction, the electromagnetic coupling means, the number of resonators employed, the operating voltages selected to be adjusted, and switching mechanism arrangement. Since many widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A reflex klystron generator for selectively providing microwave energy of a first predetermined frequency or microwave energy of a second predetermined frequency distinct and separate from said first frequency, comprising first and second cavity resonators each having an electron permeable region aligned along an axis, means for producing and directing an electron beam along said axis for progression through said electron permeable regions of said cavity resonators, means defining a reflection field-free drift space along said axis between said electron permeable regions, a reflector electrode positioned along said axis beyond said electron permeable regions for reflecting electrons directed along said axis, means for applying uni-directional voitages to said means for producing and directing said electron beam and said reflector electrode to sustain oscillation of microwave energy in said first cavity resonator with energy derived from said electron beam, means for changing the relationship between said unidirectional voltages to selectively sustain oscillation of microwave energy in said second cavity resonator with energy derived from said electron beam, the length of said means defining said field-free drift space being approximately the same as the extent of either of said electron permeable regions along said axis whereby reflection field launching of electrons effected in the field established in the vicinity of said reflector electrode is appreciably greater than field-free bunching of electrons in said field-free drift space effected when said first cavity resonator is energized.

2. Apparatus as defined in claim 1 wherein said resonators have different resonant frequencies.

3. High frequency electromagnetic energy generating apparatus comprising means including a cathode and anode for producing and directing an electron beam along an axis, a reflector electrode spaced an appreciable distance from said cathode along said axis, said electrode comprising means for producing an electric field for repelling the electrons of said beam toward said cathode, a first cavity resonator tuned to a first resonant frequency having an electron permeable region positioned along said axis between said cathode and said reflector electrode, a second cavity resonator tuned to a second resonant frequency and having an electron permeable region positioned along said axis between the electron permeable region of said first cavity resonator and said reflector electrode, the distance along said axis between said electron permeable regions being approximately the same as the extent of either of said electron permeable regions along said axis, and means connected to said reflector electrode for energizing said electrode with a uni-directional voltage to produce a reflection field for said electron beam in the vicinity of said reflector electrode.

4. High frequency electromagnetic energy generating apparatus as defined in claim 3 wherein said means for energizing said reflector electrode includes switching means for changing the unidirectional voltage applied to said reflector electrode to selectively sustain electromagnetic oscillations in said first or said second cavity -10 resonators by selective interaction of said cavity resonators with said electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 

